US7952625B2 - Calibration element for calibrating the magnification ratio of a camera, and a calibration method - Google Patents

Calibration element for calibrating the magnification ratio of a camera, and a calibration method Download PDF

Info

Publication number
US7952625B2
US7952625B2 US12/321,413 US32141309A US7952625B2 US 7952625 B2 US7952625 B2 US 7952625B2 US 32141309 A US32141309 A US 32141309A US 7952625 B2 US7952625 B2 US 7952625B2
Authority
US
United States
Prior art keywords
calibration
camera
calibration element
magnification ratio
image
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active, expires
Application number
US12/321,413
Other languages
English (en)
Other versions
US20090185038A1 (en
Inventor
Hartmut Boessmann
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Texmag GmbH Vertriebsgesellschaft
Original Assignee
Texmag GmbH Vertriebsgesellschaft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Texmag GmbH Vertriebsgesellschaft filed Critical Texmag GmbH Vertriebsgesellschaft
Assigned to TEXMAG GMBH VERTRIEBSGESELLSCHAFT reassignment TEXMAG GMBH VERTRIEBSGESELLSCHAFT ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: BOESSMANN, HARTMUT
Publication of US20090185038A1 publication Critical patent/US20090185038A1/en
Application granted granted Critical
Publication of US7952625B2 publication Critical patent/US7952625B2/en
Active legal-status Critical Current
Adjusted expiration legal-status Critical

Links

Images

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N17/00—Diagnosis, testing or measuring for television systems or their details
    • H04N17/002—Diagnosis, testing or measuring for television systems or their details for television cameras
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/93—Detection standards; Calibrating baseline adjustment, drift correction

Definitions

  • the invention relates to a calibration element for calibrating the magnification ratio of a camera, and a calibration method
  • a calibration element serving for calibrating the magnification ratio of a camera. It is preferred to make use as camera of a CCD or CMOS camera, it also being possible as an alternative to use other imaging methods. Again, whether the camera is a matrix or line camera plays no role. In particular, in cases of application where the aim is to utilize the camera to scan objects in the form of running product webs, a line camera that is aligned transverse to the running direction is completely sufficient. A calibration in the line direction is sufficient in this case. In the case of a matrix camera, the calibration can be performed in row and/or column direction depending on application. The magnification ratio of the camera is important for determining exact measured variables. However, it is dependent both on the position and on the alignment of the camera.
  • magnification ratio also changes with the thickness of the object to be examined, since the surface viewed by the camera lies closer to the camera for relatively thick objects than for relatively thin objects. These differences play a role, in particular, when objects are detected exactly using measurement technology.
  • This problem is solved by using a calibration element that has at least one calibration region. Located in this calibration region is at least one perforation or indentation that can be detected by the camera. The size or the mutual spacing of the perforation and indentation is known in this case, and so the measured variables detected by the camera can be compared with known geometric dimensions of the calibration element. It is possible in this way to determine the magnification ratio of the camera, which is dependent on the mounting and alignment.
  • this magnification ratio can also be calculated as a function of the location in the field of view of the camera, in order in this way also to correct imaging errors of the objective such as, for example, a trapezoidal distortion of the camera image.
  • the calibration element has at least one support foot whose length is selected in such a way that a variation which can be evaluated is produced in the magnification ratio of the camera image by rotating the calibration element and setting it down on the at least one support foot.
  • the at least one support foot is at least twice as long as the thickness of the calibration element in the calibration region.
  • the calibration region is located in a measurable fashion at the camera, and so the magnification ratio varies correspondingly.
  • This measurable variation in the magnification ratio then produces the desired thickness dependence of the object, and so the magnification ratio of the camera image is calibrated in this way as a function of the respective object thickness.
  • it is also intended to determine the magnification ratio as a function of the location in the field of view of the camera, in order to be able to use the camera to execute geometric measurements that are as accurate as possible.
  • the camera When detecting the calibration element of the camera, the fundamental problem arises that the camera detects the upper edge, on the one hand, and the lower edge, on the other hand, of the calibration element, the lower edge sometimes being covered by the upper edge and depending on the position of the camera.
  • the calibration element In order to avoid calibration errors because of these unknowns, in the calibration region the calibration element has such a slight wall thickness that upper and lower edges of the perforations and/or indentations produce differences in the camera image that are negligible for the calibration procedure. Because of this thin wall thickness of the calibration element in the calibration region, the camera substantially sees only one edge in the region of the perforation, and so faults in the detection of the perforation and/or indentation are excluded.
  • the calibration element having a thickness of at most 2 mm in the calibration region.
  • the upper edge and lower edge of the calibration element can in this case no longer be distinguished and so a measurement error associated therewith lies in the range of a pixel resolution of the camera, and can therefore be neglected.
  • a length of at least 10 mm has proved successful for the support foot. Particularly in the case of industrial applications with camera distances in the range of at most one meter, a sufficiently accurate measurable variation in the magnification ratio already results in this way, and so the dependence of the magnification ratio on the object thickness is sufficiently accurately calibrated in this way.
  • the at least one support foot is preferably provided in the middle of the calibration element in order to keep the latter in equilibrium when standing on the support foot.
  • a particularly effective protection of the calibration region results from a U-shaped or frame-shaped design of the support foot.
  • the support foot leads to increased mechanical strength of the calibration element and, in particular strengthens the sensitive calibration region. This also thereby increases the dimensional stability of the calibration region.
  • the calibration element has at least one indexing means.
  • This indexing means can be designed, for example, as a hole, depression, pin or the like, and corresponds to an appropriate indexing means in the detection region of the camera. It is ensured in this way that the calibration element is always arranged in an identical, reproducible way. It is thereby clear which structures of the calibration element are detected at the upper edge, and which at the lower edge of the camera. A particularly thin design of the calibration element in the calibration region is not required in this case.
  • the calibration method in accordance the invention has proved successful for calibrating the camera.
  • at least one calibration element of the aforedescribed type is laid in a field of view of the camera and the first image is produced.
  • This image then includes geometric data of the calibration element together with imaging functions of the camera that are still fundamentally unknown. These imaging functions depend, in particular, on the position and alignment of a camera, and on the focal length and setting of the camera objective.
  • the magnification ratio of the camera can be calculated by comparing the camera image with the geometric variables of the calibration element.
  • the calibration element is rotated and a further image is produced using the camera.
  • magnification ratio corresponds in the case of the first image produced to the object thickness zero and an object thickness that corresponds to the length of the support foot in the case of the second image produced. Consequently, the magnification ratio can be calculated for each desired object thickness by applying this linear function.
  • magnification ratio is calculated as a function of the location. This can be brought about, in particular, by the calibration element having a number of perforations or indentations such that in this way a plurality of geometric properties are present in the field of view of the camera. These various geometric properties can in this case enable an exact calibration even of distorted images. It is fundamentally adequate in this case to determine the dependence of the thickness of the magnification ratio as a function of location, since the functions of the magnification ratio are essentially decoupled from the thickness, on the one hand, and from the location, on the other hand.
  • the optical detection of the calibration element by the camera it is when edges to be evaluated in the images of the camera are only those in the case of which end faces of the calibration element are invisible to the camera.
  • the visibility of the end faces of the calibration element depends exclusively on the relative position between the respective end face, on the one hand, and the camera, on the other hand. If—seen perpendicular to the calibration element—the perforation or indentation is located to the left of the camera, for example, only the left-hand end faces of the perforation or indentation can be seen by the camera. In this case, only the right-hand end faces in the camera image are evaluated.
  • the perforation or indentation is, by contrast, located to the right of the camera, the left-hand edges of the perforation or indentation are evaluated. If, by contrast, the perforation is positioned both to the left and to the right of the camera, it is impossible to evaluate either of the two end faces properly. In this case, the nearest edges of the respectively neighboring perforations and/or indentations are used. It is ensured in this way that an erroneous evaluation of the lower edge of the calibration element averted from the camera is excluded.
  • FIG. 1 a two dimensional illustration of a calibration element with a camera
  • FIG. 2 the illustration in accordance with FIG. 1 with a rotated calibration element
  • FIG. 3 an enlarged illustration of a detail of the arrangement in accordance with FIG. 1 ,
  • FIG. 4 a diagram
  • FIG. 5 an alternative embodiment of the calibration element.
  • the calibration element 1 in accordance with FIG. 1 which preferably consists of an iron material, is provided in a field of view 2 of a camera 3 .
  • the camera 3 is designed in this case as a line camera such that the field of view 2 forms a long, but at the same time narrow, rectangle.
  • the calibration element 1 has a central calibration region 4 in which a number of perforations 5 are provided.
  • the camera 3 is able to detect these perforations 5 with rich contrast.
  • the limiting edges of the perforations 5 have known calibration lengths.
  • the magnification ratio of the camera 3 over the field of view 2 can be calculated from the known calibration lengths 6 and distances 7 .
  • the calibration element 1 also has a support foot 8 that extends in the shape of a frame around the calibration region 4 .
  • This support foot 8 lends an advantageous dimensional rigidity to the calibration element 1 such that the calibration region 4 can be designed with a relatively thin wall thickness.
  • the calibration region 4 and the support foot 8 are separately provided parts that are subsequently interconnected.
  • the calibration element can also be fabricated in one piece.
  • the calibration element 1 has two indexing means 22 that are designed purely by way of example in the form of bores in the exemplary embodiment in accordance with FIG. 1 .
  • Indexing means 22 ensures a reproducible, exact positioning of the calibration element 1 relative to the camera 3 , and this facilitates the detection of the perforations 5 .
  • FIG. 2 shows the arrangement in accordance with FIG. 1 , the calibration element 1 having been rotated.
  • the calibration element 1 thereby rests on the support foot 8 .
  • the calibration region 4 of the calibration element 1 comes closer to the camera 3 by a height 9 of the support foot 8 . This affects the magnification ratio of the camera 3 such that it is possible in this way to determine a dependence of the magnification ratio on an object thickness.
  • FIG. 3 shows an enlarged, sectional illustration of a detail of the arrangement in accordance with FIGS. 1 and 2 , with a cut beam path.
  • the calibration element 1 has a relatively slight wall thickness 10 in the calibration region 4 .
  • An upper edge 11 of the perforation 5 supplies a first image 14 on a photo detector 13 by means of an objective 12 of the camera 3 .
  • a lower edge 15 of the same perforation 5 is so close in this case to the upper edge 11 that it supplies the same first image 14 as the upper edge 11 in the case of the present magnification ratios.
  • the calibration region 4 lies closer to the camera 3 , and this is illustrated in FIG. 3 by dashed lines.
  • the upper edge 11 and lower edge 15 in this case supply a second image 14 ′ on the photo detector 13 that is sufficiently widely spaced from the first image 14 .
  • What is important here is not the actual position of the first image 14 and second image 14 ′ on the photo detector 13 , but only the width of the perforation 5 in the camera image. In order to obtain a high accuracy, it is preferred to measure the distances of perforations 5 lying as far apart as possible. Furthermore, it is preferred to evaluate those upper edges 11 , 16 for which the corresponding lower edges 15 , 17 are not located in the field of view of the camera 3 .
  • the first image 14 and second image 14 ′ are used to determine magnification ratios 18 as a function of the object thickness 19 of the object to be examined.
  • the first image 14 corresponds in this case to a thickness zero, while the second image 14 ′ corresponds to the height 9 .
  • Two points 20 that define a linear function 21 are obtained in this way in the diagram in accordance with FIG. 4 .
  • This linear function 21 yields the corresponding magnification ratio 18 for each object thickness 19 such that the camera 3 is calibrated for any desired object thicknesses.
  • FIG. 5 shows an alternative embodiment of the calibration element 1 in accordance with FIG. 1 .
  • the support foot 8 is designed as a central block around which the calibration region 4 extends.
US12/321,413 2008-01-21 2009-01-21 Calibration element for calibrating the magnification ratio of a camera, and a calibration method Active 2030-02-05 US7952625B2 (en)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
EP08001043.2 2008-01-21
EP08001043 2008-01-21
EP08001043 2008-01-21
EP08001442A EP2081390B1 (de) 2008-01-21 2008-01-25 Kalibrierkörper zum Kalibrieren des Abbildungsmaßstabes einer Kamera sowie Kalibrierverfahren
EP08001442.6 2008-01-25
EP08001442 2008-01-25

Publications (2)

Publication Number Publication Date
US20090185038A1 US20090185038A1 (en) 2009-07-23
US7952625B2 true US7952625B2 (en) 2011-05-31

Family

ID=40097167

Family Applications (1)

Application Number Title Priority Date Filing Date
US12/321,413 Active 2030-02-05 US7952625B2 (en) 2008-01-21 2009-01-21 Calibration element for calibrating the magnification ratio of a camera, and a calibration method

Country Status (10)

Country Link
US (1) US7952625B2 (zh)
EP (1) EP2081390B1 (zh)
JP (1) JP5174691B2 (zh)
CN (1) CN101494740B (zh)
AT (1) ATE467982T1 (zh)
CA (1) CA2649933C (zh)
DE (1) DE502008000652D1 (zh)
PL (1) PL2081390T3 (zh)
SI (1) SI2081390T1 (zh)
TW (1) TWI395052B (zh)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102207470B (zh) * 2011-03-16 2013-05-29 上海市计量测试技术研究院 一种用于校准工业计算机断层摄影系统放大倍率的标准物质
CN102855728A (zh) * 2012-09-21 2013-01-02 北京智安邦科技有限公司 一种图像型火灾探测器的自动标定方法
DE102014206580A1 (de) 2014-04-04 2015-10-08 Texmag Gmbh Vertriebsgesellschaft Materialband als kalibrationsschablone
WO2016018327A1 (en) 2014-07-31 2016-02-04 Hewlett-Packard Development Company, L.P. Camera alignment based on an image captured by the camera that contains a reference marker
US10066982B2 (en) * 2015-06-16 2018-09-04 Hand Held Products, Inc. Calibrating a volume dimensioner
CN105158877B (zh) * 2015-09-30 2017-11-14 合肥芯碁微电子装备有限公司 一种直写式光刻机缩影物镜的倍率标定方法
DE102017206971A1 (de) * 2017-04-26 2018-10-31 Krones Aktiengesellschaft Inspektionsverfahren und -vorrichtung zur bildverarbeitenden Inspektion von Behältern

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5149965A (en) * 1990-04-23 1992-09-22 Temple University Precision radiography scaling device
US6459772B1 (en) * 1999-03-18 2002-10-01 Eisenlohr Technologies, Inc. Radiographic reference marker
EP1251347A1 (de) 2001-04-18 2002-10-23 ERHARDT + LEIMER GmbH Vorrichtung zum optischen Abtasten einer laufenden Warenbahn sowie Verfahren zu deren Justierung
US6611292B1 (en) * 1999-01-26 2003-08-26 Mustek Systems, Inc. Focus controlling method and system for an image capturing system
US6915072B2 (en) * 2002-10-23 2005-07-05 Olympus Corporation Finder, marker presentation member, and presentation method of positioning marker for calibration photography

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5896204A (ja) * 1981-12-04 1983-06-08 Kawasaki Steel Corp 被圧延材の寸法測定方法
US5426509A (en) * 1993-05-20 1995-06-20 Peplinski; Robert A. Device and method for detecting foreign material on a moving printed film web
US5696591A (en) * 1996-01-05 1997-12-09 Eastman Kodak Company Apparatus and method for detecting longitudinally oriented flaws in a moving web
DE19946520B4 (de) * 1999-09-28 2010-09-16 Parsytec Ag Vorrichtung und Verfahren zur Oberflächeninspektion eines kontinuierlich zulaufenden Bandmaterials
JP2002286425A (ja) * 2001-03-23 2002-10-03 Omron Corp 変位センサ
JP2003148912A (ja) * 2001-11-13 2003-05-21 Hitachi Metals Ltd 光学式寸法測定方法
CN100374816C (zh) * 2003-05-28 2008-03-12 富士机械制造株式会社 电子元件安装机的拍摄图像处理装置及拍摄图像处理方法
TWI274845B (en) * 2005-10-04 2007-03-01 Univ Nat Formosa Equipment for detecting the object corner and distance using a sole lens

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5149965A (en) * 1990-04-23 1992-09-22 Temple University Precision radiography scaling device
US6611292B1 (en) * 1999-01-26 2003-08-26 Mustek Systems, Inc. Focus controlling method and system for an image capturing system
US6459772B1 (en) * 1999-03-18 2002-10-01 Eisenlohr Technologies, Inc. Radiographic reference marker
EP1251347A1 (de) 2001-04-18 2002-10-23 ERHARDT + LEIMER GmbH Vorrichtung zum optischen Abtasten einer laufenden Warenbahn sowie Verfahren zu deren Justierung
US6915072B2 (en) * 2002-10-23 2005-07-05 Olympus Corporation Finder, marker presentation member, and presentation method of positioning marker for calibration photography

Also Published As

Publication number Publication date
CA2649933A1 (en) 2009-07-21
JP2009175147A (ja) 2009-08-06
CN101494740A (zh) 2009-07-29
TWI395052B (zh) 2013-05-01
PL2081390T3 (pl) 2010-09-30
EP2081390B1 (de) 2010-05-12
DE502008000652D1 (de) 2010-06-24
EP2081390A1 (de) 2009-07-22
CA2649933C (en) 2013-04-02
CN101494740B (zh) 2011-06-22
SI2081390T1 (sl) 2010-10-29
US20090185038A1 (en) 2009-07-23
JP5174691B2 (ja) 2013-04-03
ATE467982T1 (de) 2010-05-15
TW200933287A (en) 2009-08-01

Similar Documents

Publication Publication Date Title
US7952625B2 (en) Calibration element for calibrating the magnification ratio of a camera, and a calibration method
US9046349B2 (en) Method and device for contactless determination of the thickness of a web of material, including correction of the alignment error
JP5707041B2 (ja) 厚さ測定のための方法及び装置
US4074131A (en) Apparatus for measuring or setting two-dimensional position coordinates
JP2015017844A5 (zh)
CN105698686A (zh) 一种裂缝测宽仪示值误差检测装置及方法
JP6606441B2 (ja) 検査システムおよび検査方法
JP2000252203A (ja) アライメントマーク及びアライメント方法
US6819789B1 (en) Scaling and registration calibration especially in printed circuit board fabrication
CN109073991A (zh) 在测量桌上检测掩模夹具的位置的方法
US20090153880A1 (en) Optical system for detecting motion of a body
JP6203502B2 (ja) 加工品に対して加工工具を位置決めするための構造および方法
TWI501049B (zh) 對於分區曝光之物體而測量其中一區之相對局部位置誤差之方法與裝置
JP6730857B2 (ja) 段差高さゲージ、基準面測定方法、及び基準面測定装置
KR20130102499A (ko) 측정기와, 측정 오차의 보정 방법
JP7126146B2 (ja) 非破壊試験方法
US7154110B2 (en) Systems and methods for improving calibration of a linear array sensor
US8096163B2 (en) Verifying the calibration status of an optical tracking system
JP5208681B2 (ja) 斜入射干渉計における測定感度の校正方法
US20210036384A1 (en) Non-Destructive Inspection Method
JP6965795B2 (ja) 距離計校正方法及びそれに用いる校正治具
JP5950760B2 (ja) 干渉形状測定機構の校正方法
JP2007218755A (ja) 光電式エンコーダのアライメント角度検査装置
JP2024000912A (ja) 形状測定装置の校正方法
TWI582400B (zh) 檢測靶板、光學檢測裝置及光學檢測方法

Legal Events

Date Code Title Description
AS Assignment

Owner name: TEXMAG GMBH VERTRIEBSGESELLSCHAFT, SWITZERLAND

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:BOESSMANN, HARTMUT;REEL/FRAME:022363/0433

Effective date: 20090130

STCF Information on status: patent grant

Free format text: PATENTED CASE

FPAY Fee payment

Year of fee payment: 4

MAFP Maintenance fee payment

Free format text: PAYMENT OF MAINTENANCE FEE, 8TH YEAR, LARGE ENTITY (ORIGINAL EVENT CODE: M1552); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

Year of fee payment: 8

MAFP Maintenance fee payment

Free format text: PAYMENT OF MAINTENANCE FEE, 12TH YEAR, LARGE ENTITY (ORIGINAL EVENT CODE: M1553); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

Year of fee payment: 12